AP Staining of Degenerating Mammary Glands. Day 0 mammary glands (upper left and right panels) and day 4 mammary glands (lower left and right panels) are shown. Day 0 control mammary gland cells (substrate for AP was omitted in the reaction; upper left panel) show no positive AP staining, while there is faint AP-positive staining in the day 0 experimental slide (upper right panel). The day 4 experimental mammary gland shows marked staining for AP and altered cytoplasmic morphology (lower right panel) relative to the control slide (lower left panel). The magnification for all of the panels was 400X.